Lithium-cation conductivity and crystal structure of lithium diphosphate

The electrical conductivity of lithium diphosphate Li4P2O7 has been measured and jump-like increasing of ionic conductivity at 913 K has been found. The crystal structure of Li4P2O7 has been refined using high temperature neutron diffraction at 300–1050 K. At 913 K low temperature triclinic form of Li4P2O7 transforms into high temperature monoclinic one, space group P21/n, a=8.8261(4) Å, b=5.2028(4) Å, c=13.3119(2) Å, β=104.372(6)°. The migration maps of Li+ cations based on experimental data implemented into program package TOPOS have been explored. It was found that lithium cations in both low- and high temperature forms of Li4P2O7 migrate in three dimensions. Cross sections of the migrations channels extend as the temperature rises, but at the phase transition point have a sharp growth showing a strong "crystal structure – ion conductivity" correlation. -- Graphical abstract: Crystal structure of Li4P2O7 at 950 K. Red balls represent oxygen atoms; black lines show Li+ ion migration channels in the layers perpendicular to [001] direction. Highlights: • Structure of Li4P2O7 has been refined using high temperature neutron diffraction. • At 913 K triclinic form of Li4P2O7 transforms into high temperature monoclinic one. • The migration maps of Li+ implemented into program package TOPOS have been explored. • Cross sections of the migrations channels at the phase transition have a sharp growth